Spare Tire ?

For the rear you would definitely want to keep the WD bars on - they move weight to the front tires, reducing the wight on the rear. If it was a front tire, you'd probably want to leave them off for the same reason... (You'd also want to go very slow with flashers and get off at the first exit with a tire shop, to keep that small spare from getting too hot and to minimize the danger if it can't handle the load.)

Personally, I'd leave the trailer (if possible), get the tire replaced, then return and get the trailer. Fortunately, my Sienna has a full size spare.